Recently in association with the progress in the technology for information networking, there are the strong needs for more advanced and sophisticated functions of, lower power consumption in, and size and weight reduction of equipment for information communications, and to satisfy the needs, now it is required to develop semiconductor devices having a higher processing speed and realize a higher degree in circuit integration. Improvement in performance of semiconductor devices has been realized by miniaturization of circuit design, but now device circuits are designed with the dimensions at a submicron level, and the integration degree is higher as compared to that in the past, but the power consumption has disadvantageously increased because of increase in the wiring capacitance, and there occur such problems as wiring delay or cross talk, and therefore further improvement by miniaturization of a circuit design can not be expected. Especially, in a semiconductor device with multilayered wirings designed under a rule of 0.25 microns, a space between metal wires becomes narrower, and therefore impedance in the metal wiring due to electrostatic induction increases, and there are serious concerns about the possibility of delay in response speed and increase in power consumption. To overcome the problems as described above, it is required to minimize a dielectric constant of an interlayer insulating film between a semiconductor substrate and a metal wiring layer such as an aluminum wiring layer or a copper wiring layer or between the metal wiring layers.
The present inventors made strenuous efforts to solve the problems as described above, and found that an amorphous silica-based coating film with high strength and having the specific dielectric constant of 3.0 or below and even 2.5 or below and the Young's modulus of 6.0 GPa or more can be formed by using a coating liquid for forming an amorphous silica-based coating film with a lower dielectric constant containing a silicon compound obtained by hydrolyzing tetraalkyl orthosilicate (TAOS) and specific alkoxysilane (AS) in the presence of tetraalkyl ammonium hydroxide (TAAOH), and made a patent application based on the finding (described in Patent document 1). Furthermore the inventors found, in relation to the invention described above, (1) a method for forming a amorphous silica-based coating film having a low dielectric constant by applying a coating liquid containing the silicon compound on a substrate and thermally processing the coating liquid at the temperature in the range from 80 to 350° C. and then curing the coating liquid at the temperature in the range from 350 to 450° C., and (2) a method for forming an amorphous silica-based coating film by applying a coating liquid containing the silicon compound on a substrate, thermally processing the coating liquid at the temperature in the range from 80 to 350° C., and then irradiating an electron beam for curing the coating liquid, and made a patent application based on the finding (as described in Patent document 2 and Patent document 3).
Now it is possible to form an interlayer insulating film which can satisfy the needs and demands by semiconductor manufacturers as described above, and in association with the techniques newly developed, it is required to provide materials for formation of a protective film for semiconductor processing such as a CMP sacrifice film or an etching stopper film having excellent abrasion resistance as well as a high film strength and a low specific dielectric constant allowing for a high freedom in selection of conditions for etching and furthermore excellent in such properties as adhesiveness, chemical resistance, ashing resistance, plasma resistance, heat resistance, moisture resistance, and stability.
In the conventional technology, as the protective films, generally a silicon dioxide (SiO2) film, a silicon nitrate (SiN) film, a silicon carbide (SiC) film, a silicon carbide nitrogen (SiCN) film and the like are used, and the films are formed by the gas phase growth method based on the plasma CVD (Plasma Chemical Vapor Deposition). The protective films as described above have, however, the defect that the specific dielectric constant is around 3.8 in a case of the silicon dioxide film or 4.0 or more in other films, and the effective dielectric constant of the entire semiconductor substrate becomes disadvantageously higher even when a specific dielectric constant of the interlayer insulating film is 3.0 or below.
In contrast, there has been proposed a method for formation of a protective film for semiconductor processing such as a CMP sacrifice film or an etching stopper film by using a coating liquid containing an organic silicon polymer such as polycarbosilane for the purpose to further lower a specific dielectric constant of the protective film (the so-called coating method) (as described in Patent document 4 and Patent document 5). The protective films formed by using the coating liquid as described above have the specific dielectric constant of 3.0 or more, and the film strength is not always high, and therefore it can not be said that the protective films satisfy the needs of the semiconductor manufacturers.
Patent document 1: JP 2004-149714 A
Patent document 2: JP 2004-153147 A
Patent document 3: Specification of JP Application No. 2004-141749
Patent document 4: JP 2004-186610 A
Patent document 5: JP 2004-186611 A